Newsbrief: Independent developer and publisher Tripwire Interactive has sold 1.1 million copies of Killing Floor since the standalone version of the co-op first-person shooter released for PC in 2009.

The studio says the game, which began as an Unreal Tournament 2004 mod that debuted in 2005, is still selling strongly despite its age. Georgia-based Tripwire has also sold nearly 2 million downloadable content packs for Killing Floor.

Tripwire's PC games, which include the Red Orchestra series, have sold more than 2 million copies so far since the company was founded in 2005. It will release Rising Storm later this year, and has begun publishing externally developed titles like ACE Team's Zeno Clash on PC.